Most weekends I don't give any thought to driving through local canyons after a beach dive, since we don't dive deeper than about 40 feet for under 90 minutes, but the weekend before last I joined a PADI instructor deep specialty class and we did two dives - 120 feet, then 95 ft. No deco, but both on air. Later in the afternoon, several of us independently drove to the other side of the hill, which got up to about 1300 ft and we all went around to go through a canyon road with a lower maximum elevation, even though it was out of the way. Last weekend, I asked Karl Huggins what his advice would be, and he suggested treating the dives as altitude dives in terms of NDL planning, with the NDL figured based on altitude for the highest elevation to drive afterwards. Is this the recommended approach (it made sense to me), or is there a better way to plan? If this is the right way to do it, does time at sea level before driving over the canyon count as off gassing, since nitrogen should be getting out of my body, or on gassing, since I'm below the planned highest elevation for my drive?